1. Field of the Invention
The invention relates to a pulling device for the removal of ground embedded structures and, more particularly, to an improved pulling device that provides maximum lifting force at the start of the pull and maximum height near the end of the pull, the force and lift being provided by a hydraulically actuated piston and an eccentrically pivoted wheel.
2. Description of the Prior Art
A variety of pulling devices have been developed which provide a force to remove tree stumps and the like. Typically these devices utilize a pulley or similar system. Such devices are often driven by hydraulic or electrical motors, combustion engines, or extendible hydraulic cylinders.
One such prior art pulling device utilizes an arrangement of cables which rotate a pulley that has an eccentrically mounted arm. The arm attaches to a chain which is attached to the stump. As the pulley is rotated and lifted the structure is pulled. The device is self-contained and the cable is pulled by a horse, tractor or other moving vehicle.
Another such prior art device utilizes the power from a rod extending from a hydraulic cylinder to provide the lifting force to remove a stump. The device has a ground engaging bifurcated platform which supports a pivoted boom. A cable is wrapped through the boom over a pulley and down toward the ground. The cable is attached to the stump and the hydraulic cylinder assembly provides retraction of the cable along the boom to pull the stump.
Such prior art devices, however, are not generally applicable to the removal of all ground embedded structures, particularly posts or other structures of significant length such as those used to support fencing, road signs and traffic control devices. In particular, the prior devices fail to provide optimum force or lift for the removal of ground embedded structures. For maximum efficiency, a device adaptable for pulling a wide variety of ground embedded structures, including posts, should provide a maximum force when the structure is fully engaged in the ground and its resistance to removal, or yield resistance, is the greatest. The force should decline as the structure yields and is lifted. The lift or height provided to the structure should then be as great as possible so that the structure can be completely disengaged from the ground.
For greater maneuverability the apparatus should also be compact and relatively lightweight. Ideally, it should be operable in relation to a tractor without transmitting the pulling force to the tractor.
The pulling device of this invention provides maximum pull when a ground embedded structure's yield resistance is the greatest and maximum lift to fully remove such structures, particularly long posts, from the ground. The invention utilizes the eccentric rotation of a particularly configured structure to apply pulling force with a pull chain and a varying rotational torque means.